ACI ITG 4 2R:2006 download.Materials and Quality Considerations for High-Strength Concrete in Moderate to High Seismic Applications.
1.1—Background
The origin of ACI’s Innovation Task Group (ITG) 4. High-Strength Concrete for Seismic Applications, can be traced back to an International Conference of Building Officials (ICBO) (now International Code Council [ICC])
Evaluation Report titled “Seismic Design Utilizing High- Strength Concrete (ER-5536)” (ICC Evaluation Service. Inc. 2004). Evaluation Reports (ERs) are issued by Evaluation Service subsidiaries of model code groups. An ER essentially states that, although a particular method, process. or product is not specitically addressed by a particular edition of a certain model code. it is in compliance with the requirements of that particular edition of that model code.
ER-5536, first issued in April 2001, was generated for the seismic design of moment-resisting frame elements using high-strength concrete. High-strength concrete was defined as “normalweight concrete with a design compressive strength greater than 60(X) psi (41.3 MPa) and up to a maximum of I 2.(XX) psi (82.7 MPa).” It was based on research carried out at the University of Southern California and the University of California at San Diego to support building construction in Southern California using concrete with compressive strengths greater than 6(XX) psi (41 MPa). ER-5536 is available on the ICC website .
The Portland Cement Association (PCA) performed a review of the aforementioned document, which brought up several concerns that focused on inconsistencies between the ER and existing industry documents in two primary areas:
material and structural aspects. Irrespective of those concerns, it was evident that the ER had been created because quality assurance and design provisions are needed by local jurisdictions in cities such as Los Angeles to allow the use of high-strength concrete in a safe manner. ACI has assumed a proactive role in the development of such provisions with the goal of creating a document that can be adopted nationwide.
Within ACI, Committee 363, High Strength Concrete, was considered the best choice to develop the section addressing materials quality considerations aspects of the document. while ACI Committee 318-H. Structural Concrete Building Code—Seismic Provisions, was considered the logical choice to address seismic detailing aspects. Because ACt Committee 318-H isa subcommittee of a code-writing body. the development of a technical document of this kind is not part of its intended mission. Also, producing a document by a technical committee is typically a lengthy process. Based on hese limitations, a request was made to fonn an Innovation Task Group (ITG) that would have the advantage of completing the desired product within a shorter timeline. In response to the request. the Technical Activities Committee (TAC) of ACI approved the formation of ITG 4. Following the approval by TAC. David Darwin. then Chair of the TAC Technology Transfer Committee (1TIC). established the mission of the ITG. The mission is to develop an ACt document that addresses the application of high-strength concrete in structures located in areas of moderate and high seismicity. The document is intended to cover structural design. material properties. construction procedures, and quality-control measures. It is to be written or contain example language in a format that will allow building officials to approve the use of high-strength concrete in projects that are being constructed under the provisions of ACt 301 and 318.
CHAPTER 3—GLOSSARY OF TERMS
The terminology used in this document is in substantial agreement with ACt I 16R and 318. When the definitions of a term in ACI I 16R and 318 differ. the ACt 318 definition is adopted.
admixture—material other than water. aggregate. or hydraulic cement, used as an ingredient of concrete and added to concrete before or during mixing to modify its properties.
aggregate—granular material, such as sand, gravel, crushed stone, and iron blast-furnace slag. used with a cementing medium to form a hydraulic cement concrete or mortar.
alkali-aggregate reaction (AAR)—chemical reaction in either mortar or concrete between alkalies (sodium and potassium) from portland cement or other sources and certain constituents of some aggregates: under certain conditions. deleterious expansion of concrete or mortar may result.
alkali-silica reaction (ASR)—the reaction between the alkalies (sodium and potassium) in portland cement and certain siliceous rocks or minerals, such as opaline chert, strained quartz, and acidic volcanic glass. present in some aggregates: the products of the reaction may cause abnormal expansion and cracking of concrete in service.
bleeding—the autogenous flow of mixing water within, or its emergence from, newly placed concrete or mortar: caused by the settlement of the solid materials within the mass: also called water gain.
cementitious materiaLs—materials that have cementing value when used in concrete, either by themselves, such as portland cement, blended hydraulic cements, and expansive cement, or in combination with fly ash, other raw or calcined natural pozzolans. silica fume, and/or ground-granulated blast-furnace slag.
concrete, compressive strength of—the measured maximum resistance of a concrete or mortar specimen to axial compressive loading: expressed as force per unit cross-sectional area: or the specified resistance used in design calculations.
concrete, high-strength——concrete that has a specified compressive strength of 6000 psi (41 MPa) or greater.
concrete, hydraulic-cement—rn i xture of portland cement or any other hydraulic cement, fine aggregate, coarse aggregate, and water, with or without admixtures.
concrete, specified compressive strength of (f )— compressive strength of concrete used in design.
consistency—the relative mobility or ability of freshly mixed concrete or mortar to flow; the usual measurements are slump or spread for Concrete, flow for mortar or grout. and pene(ration resistance for neat cementflious paste.
creep—time-dependent increase in deformation due to sustained load; determined in accordance with ASTM C 512.
creep coefficient—strain due to creep divided by the initial elastic strain.
curing provision of moisture and appropriate temperatures for sufficient time for the concrete to develop the required properties.
delayed etiringite formation (DEF)—a form of internal sulfate attack caused by the suppression of normal ettringite
6.5.1 Fine aggregaies—Fine aggregate, or sand, has a significant effect on mixture proportions. The fine aggregate contains a much higher surface area for a given mass than the coarse aggregate. Because the surface area of aggregate particles should be coated with a cementitious paste, the proportion of tine-to-coarse aggregate can have a direct effect on paste requirements. Furthermore, the shape of tine aggregate particles may be spherical, subangular. or very angular. Particle shape can alter paste requirements even though the net volume of the fine aggregate remains the same.
The sand equivalent value for fine aggregates (ASTM D 2419) for use in high-strength concrete should not be less than 85. The fineness modulus of fine aggregate for use in high-strength concrete should be between 2.5 and 3.2.
The gradation of the fine aggregate plays an important role in the properties of the plastic and the hardened concrete. For example, if the gradation is such that an overabundance of particles is retained on the No. 50 and 100(300 and 150 jim) sieve sizes, the workability will be improved, hut more paste will be needed because of the increased surface area of the fine aggregates. It is sometimes possible to blend fine aggregates from different sources to improve their gradation and their capacity to produce high-strength concrete. High- strength concrete has been produced using blended sands consisting of manufactured and natural fine aggregates.
Low fine aggregate contents in combination with high coarse aggregate contents have resulted in a reduction in paste requirements for high-strength concrete, and are generally more economical. Such proportions have also made it possible to produce higher strengths for a given amount of cementitious material. If the proportion of fine aggregate is too low. however, there may be serious problems with workability.
6.5.2 coarse aggregates—In proportioning normal- strength concrete mixtures, the optimal quantity and size of coarse aggregate are functions of the maximum size and fineness modulus of the fine aggregate. High-strength concrete mixtures have a high cementftious material content, and thus are not so dependent on the fine aggregate to supply tines for lubrication of the fresh concrete and for particle packing.
In general. the smallest-size coarse aggregate produces the highest-strength concrete for a given •/crn. The selection of coarse aggregate size may he intluenced by requirements other than strength. The use of a coarse aggregate with a larger nominal maximum size is often needed to increase the modulus of elasticity or to decrease the creep. shrinkage, or heat of hydration of the concrete.
The quantities of coarse aggregate in Table 6. I are recommended for initial proportioning. The values given are expressed as a fraction of the dry-rodded unit weight and based on the nominal maximum coarse-aggregate size, and used with tine aggregates having a fineness modulus between 2.5 and 3.2.
1 8.2—Cited references
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(in French)
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